JP4413972B2 - Manufacturing method of fiber grating - Google Patents

Description

The present invention relates to a method for producing a fiber grating.

With the arrival of the broadband era, further increase in data transmission volume is required. Therefore, a wavelength division multiplexing transmission system {WDM (Wavelength Division Multiplexing) transmission system} that multiplexes and transmits a plurality of lights having different wavelengths has come into practical use.

As one of key devices in this WDM transmission system, an optical amplifier such as an EDFA capable of collectively amplifying the multiplexed optical signal without performing photoelectric conversion has been developed.
However, in the WDM transmission system, if there is a level deviation in the transmitted signal light of each wavelength, the optical signal may be deteriorated and the transmission distance and transmission band may be reduced. Therefore, optical amplifiers such as EDFA are required to equalize (flatten) the gain characteristics in the transmission band.

Accordingly, in order to compensate for the gain characteristic having the wavelength dependency (gain wavelength dependency), a filter device having a transmission loss-wavelength characteristic opposite to the gain-wavelength characteristic of the optical amplifier is combined with the optical amplifier. It has been put into practical use to flatten the gain characteristic of an amplifier. In particular, as this filter device, a long period fiber grating (LPG) having a grating pitch of about 100 μm to 1000 μm is often used as a gain equalizer.

In order to realize a gain equalizer using a long-period fiber grating, a combination of a long-period fiber grating (Uniform LPG) having a uniform pitch of interference fringes and a uniform long-period fiber grating and a phase shift are used. There are two possible ways of using long period fiber gratings (Phase Shift LPG) in combination.

As an example, an example of a gain equalizer having a transmission loss-wavelength waveform as shown in FIG. 11 as a target characteristic will be described. Here, the vertical axis of FIG. 11 is transmission loss (Loss), and the unit is dB. The horizontal axis is the wavelength and the unit is nm.

First, as an example of a gain equalizer in which uniform long-period fiber gratings are combined, an embodiment of a gain equalizer in which four uniform long-period fiber gratings (LPG1 to LPG4) shown in FIG. 12 are connected will be described. Uniform long-period fiber gratings are fused and joined. The lengths of the four uniform long-period fiber gratings are as follows:
LPG1: 89mm, LPG2: 91mm, LPG3: 46mm, LPG4: 88mm

FIG. 13 shows the transmission loss-wavelength waveform of each of LPG1 to LPG4 and the transmission loss-wavelength waveform of a gain equalizer that combines them. Here, the vertical axis and the horizontal axis of the graph of FIG. 13 are the same as those of the target characteristics of FIG.
It can be seen that the transmission loss-wavelength waveform of the gain equalizer shown in FIG. 13 substantially matches the target characteristics.

As shown in FIG. 14, another method is a gain equalizer in which LPG1, which is a uniform long period fiber grating, and LPG2, which is a phase shift long period fiber grating, are coupled by fusion. The lengths of the fiber gratings LPG1 and LPG2 are as follows.
LPG1: 89mm, LPG2: 46.22mm

FIG. 15 shows transmission loss-wavelength waveforms of LPG1 and LPG2, and a transmission loss-wavelength waveform of a gain equalizer obtained by combining these. Here, the vertical axis and the horizontal axis of the graph of FIG. 15 are the same as those of the target characteristics of FIG.
It can be seen that the transmission loss-wavelength waveform of the gain equalizer shown in FIG. 15 substantially matches the target characteristics as in the case of FIG.

Next, a manufacturing method of the long period fiber grating constituting the gain equalizer will be described. Usually, by irradiating an optical fiber with an ultraviolet laser, the refractive index of the optical fiber is changed to form a fiber grating. A grating having a pitch of about 100 μm to 1000 μm is usually referred to as a long period fiber grating.

In order to increase the photosensitivity of the optical fiber forming the fiber grating including the long-period fiber grating, a hydrogen treatment in which the optical fiber is impregnated with hydrogen may be performed before the ultraviolet laser irradiation.

As described above, an amplifier gain equalizer having a predetermined target characteristic by combining long-period fiber gratings has been conventionally used, but the following problems have occurred.

Usually, a reinforcing member (package) is required for each long-period fiber grating constituting the gain equalizer. For example, in the case of the gain equalizer shown in FIG. 12, four reinforcing members are required, and in the case of the gain equalizer shown in FIG. 14, two reinforcing members are required. Since the size of the reinforcing member itself is about several centimeters, as a result, the size of the gain equalizer becomes considerably large, causing a practical problem.

The transmission loss of the long-period fiber grating-the bandwidth of the peak band of the wavelength waveform and the grating length have a negative correlation. Therefore, when realizing a gain equalizer having a target characteristic with a short bandwidth, a gain equalizer is configured when a conventional uniform long-period fiber grating or phase-shifted long-period fiber grating is used. The length of the long-period fiber grating is increased.

Therefore, when the gain equalizer is actually applied, it is often necessary to be small in size, but when a target characteristic with a short bandwidth is required, a plurality of reinforcing members are necessary. Since the length of the long-period fiber grating itself becomes longer, it is difficult to realize a gain equalizer that does not have a practical problem.

Further, as described above, in order to improve the photosensitivity, hydrogen treatment that impregnates hydrogen in the optical fiber may be performed in forming the long-period fiber grating. In this case, the following problems occur. appear.

The amount of change in refractive index after irradiation of the optical fiber has a correlation with hydrogen loss after hydrogen treatment of the optical fiber. An optical fiber subjected to high-pressure hydrogen treatment is irradiated with an ultraviolet laser to form a long-period fiber grating, and then annealed to remove hydrogen. During this process, the center wavelength of the long-period fiber grating varies greatly toward the short wavelength side due to the influence of hydrogen in the fiber. That is, there arises a problem that the center wavelength largely fluctuates to the short wavelength side after the ultraviolet laser irradiation and after the annealing. In addition, the fluctuation value varies greatly for each fiber grating, making it difficult to manufacture a stable long-period fiber grating.

In order to obtain a low hydrogen concentration, a method of performing a hydrogen treatment at a low pressure or a method of performing a hydrogen treatment in a short time can be considered, but since temperature dependence is large, temperature management when performing the hydrogen treatment is also necessary. There's a problem.

In addition, if a photosensitive fiber is used, it is possible to form a predetermined fiber grating without performing hydrogen treatment. However, compared to the case where hydrogen treatment is performed, more light irradiation is required to form a fiber grating. This is necessary and reduces productivity. There is another problem that the refractive index modulation is small.

Accordingly, an object of the present invention is to provide a method for manufacturing a fiber grating that solves the conventional problems, controls hydrogen loss in an optical fiber, and suppresses fluctuations in the center wavelength of the fiber grating after annealing. is there.

This inventor repeated earnest research in order to solve the conventional problem mentioned above. As a result, as shown below, the inventors have discovered a method for manufacturing a fiber grating that solves the problems that cannot be solved by the prior art and that suppresses fluctuations in the center wavelength of the fiber grating after annealing.

According to a first aspect of the fiber grating manufacturing method of the present invention, the first step of impregnating the optical fiber with hydrogen by high-pressure hydrogen and pre-annealing for a predetermined time during which the concentration of hydrogen contained in the optical fiber is reduced to a predetermined concentration are performed. and step 2 of performing, step 3 of forming a fiber grating by irradiating ultraviolet laser to the optical fiber, and step 4 is annealed for removal of the hydrogen from said optical fiber comprises a after the step 3 And the time for performing the pre-annealing is controlled so that the fluctuation amount of the center wavelength of the fiber grating after the step 4 is 10 nm or less .

2. The fiber grating manufacturing method according to claim 1 , wherein in the second aspect of the fiber grating manufacturing method of the present invention, in the step 1, the optical fiber is impregnated with hydrogen by high-pressure hydrogen of approximately 15 MPa. It is.

The fiber grating fabricating method of the present invention performs a pre-annealing in order to remove the hydrogen impregnated in the optical fiber, so that a predetermined hydrogen loss can be obtained by controlling the pre-annealing time, after ultraviolet laser irradiation and the variation of the center wavelength of the fiber gray tee ring after annealing, can produce a superstructure long period fiber grating can be sufficiently suppressed.

In addition, fiber gratings manufactured by properly controlling pre-annealing time In sub-nano order wavelength control is possible.

A gain equalizer using the superstructure long-period fiber grating of the present invention. Has a short fiber grating length and requires only one reinforcing member. Realizing a smaller gain equalizer than ever before with an overloss-wavelength waveform Can do.

First, an embodiment of a gain equalizer of a small package that can cope with a target characteristic with a short bandwidth will be described in detail with reference to the drawings.

In order to achieve a target characteristic with a short bandwidth, there is a problem that the length of the gain equalizer becomes too long when a conventional uniform long period fiber grating or phase shift LPG is used.

Therefore, the present invention proposes a gain equalizer that uses a super-structure long-period fiber grating (Super-Structure LPG) instead of a conventional long-period fiber grating or the like.
FIG. 1 shows the structure of a superstructure long-period fiber grating. L1 shown in FIG. 1 is the length of the portion where the grating is formed by the irradiation of the ultraviolet laser, and L2 is the length of the portion where the grating is not formed. In FIG. 1, N gratings having a length L1 and the same configuration are formed.

The period P1 of the part where the grating of length L1 is formed is usually on the order of several hundred μm, and the length L2 of the part where the grating is not formed is considerably longer than P1. Usually, the length of L2 is 10 times or more of P1.
Moreover, as a length of L2, 5 mm-150 mm is a suitable range.

Table 1 shows an exemplary structure of a superstructure long-period fiber grating. There are five types of superstructure long-period fiber gratings from SSLPG1 to SSLPG5. The length of L1 is the same at 5 mm, and the length of L2 is different. As the numbers of SSLPG1 to SSLPG5 increase, the length of L2 increases. The number N of gratings of length L1 is 6 and the same.
The total length L of the superstructure long-period fiber grating is expressed by L = N × L1 + (N−1) × L2, as is apparent from FIG.

Here, FIG. 2 shows a transmission loss-wavelength waveform of the above-described superstructure long-period fiber gratings SSLPG1 to SSLPG5. The vertical axis of the graph is transmission loss (Loss), and the unit is dB. The horizontal axis is the wavelength (Wavelength) and the unit is nm.
The uniform long-period fiber grating whose characteristics are shown in FIG. 2 together with the superstructure long-period fiber grating is a long-period fiber grating having a grating length L of 30 mm.

The following can be understood from the transmission loss-wavelength waveform shown in the graph of FIG.
(1) The center wavelength of the peak of the superstructure long-period fiber grating is related not only to the period of the grating but also to the distance (L2) between the parts where the grating is formed.
(2) When the center wavelength of the superstructure long-period fiber grating coincides with the center wavelength of a uniform long-period fiber grating having the same period, the transmission loss is maximized. The farther the center wavelength of the superstructure long-period fiber grating is from the center wavelength of the uniform long-period fiber grating having the same period, the smaller the transmission loss.
(3) Although the center wavelength and transmission loss peak value of superstructure long-period fiber gratings SSLPG1 and SSLPG5 are substantially the same, SSLPG5 has a narrower bandwidth. SSLPG1 has a length of 55 mm, while SSLPG5 has a length of 69.5 mm. Therefore, comparing this bandwidth with the length of the superstructure long-period fiber grating, it can be seen that there is a negative correlation between the bandwidth and the grating length.

Table 2 shows the structure of another superstructure long-period fiber grating embodiment. SSLPG1 to SSLPG4, which are superstructure long-period fiber gratings, have the same length L2 of 7.91 mm where no grating is formed. Further, the total length (N × L1) of the portion where the grating is formed is the same. However, the number N of the gratings having the length L1 is 2 to 7 different values.

Here, FIG. 3 shows a transmission loss-wavelength waveform of the above-described superstructure long-period fiber grating. The vertical axis of the graph is transmission loss (Loss), the unit is dB, the horizontal axis is wavelength (Wavelength), and the unit is nm.
The uniform long-period fiber grating whose characteristics are shown in FIG. 3 is a grating having a grating length L of 30 mm.

From the transmission loss-wavelength waveform in the graph of FIG.
(1) If the length L2 of the portion where the grating is not formed is constant, the center wavelength of the main peak is also constant.
(2) In a fiber grating having the same total length (NxL1) of the portion where the grating is formed, the bandwidth of the peak of transmission loss becomes narrower as N increases.
In addition, the distance between the main peaks also increases.
(3) Accordingly, it can be seen that if a superstructure long-period fiber grating is used, a transmission loss profile with a narrower bandwidth can be realized with the same irradiation length (NxL1) as a uniform long-period fiber grating.

As described above, by combining this superstructure long-period fiber grating, a small package gain equalizer corresponding to a narrow bandwidth can be realized. Next, an embodiment of this gain equalizer will be described.

As a target characteristic of transmission loss-wavelength waveform, consider a gain equalizer that realizes the target characteristic shown in FIG.
FIG. 4 shows the configuration of this gain equalizer. SSLPG1 is a superstructure long-period fiber grating with the number N = 2 of gratings having a length L1, and LPG2 is a uniform long-period fiber grating, and has the following structure. SSLPG1: Length L1: 16 mm of the portion where the grating is formed,
Length L2 where the grating is not formed: 30.25 mm
Number of L1 N: 2
Full length L: 62.25mm
LPG2: Total length L: 27 mm
Here, LPG2 is formed in a portion (L2) where the grating of SSLPG1 is not formed.
Both are single mode fibers (SMF), SSLPG1 uses the 4th order quadruple mode, and LPG2 uses the 5th order quadruple mode.

FIG. 5 shows the target transmission loss-wavelength waveform and the transmission loss-wavelength waveform of SSLPG1, LPG2, and the gain equalizer. The vertical axis of the graph is transmission loss (Loss), and the unit is dB. The horizontal axis is the wavelength, and the unit is nm.

As shown in FIG. 5, the target characteristics and the transmission loss-wavelength waveform of the gain equalizer are almost the same. Therefore, it is proved that by using a superstructure long-period fiber grating, a gain equalizer that conventionally required to connect a plurality of long-period fiber gratings can be built in one superstructure long-period fiber grating. It was done.
Therefore, since only one reinforcing member is required, a small gain equalizer that solves the conventional problems can be obtained.

In this embodiment, a single mode fiber is used. However, if a special fiber such as a fiber having a small cladding layer diameter or a high refractive index of the core layer is used, the length of the fiber grating can be further shortened. there is a possibility.

A gain equalizer using the superstructure long-period fiber grating of the present invention shown in FIG. 4 and four uniform long-period fiber gratings (L1 to L4) shown in FIG. Compare equalizers.
The transmission loss-wavelength waveforms of both gain equalizers almost coincide with the target characteristics.

Next, the lengths of the gain equalizers are compared.
In the case of the present invention shown in FIG. 4, since LPG2 is formed in the L2 portion of SSLPG1, the total length L is 62.25 mm, which is the length of SSLPG1 itself.
On the other hand, in the conventional type shown in FIG. 12, L = LPG1 + LPG2 + LPG3 + LPG4 = 314 mm.
Therefore, the gain equalizer using the above-described superstructure long-period fiber grating is about 1/5 the length of the conventional gain equalizer using a uniform long-period fiber grating, and has the same characteristics. Obtainable.

Compared with the embodiment of the gain equalizer shown in FIG. 13 in which LPG1 of uniform long-period fiber grating and LPG2 which is phase-shifted long-period fiber grating are combined. Also in the conventional gain equalizer shown in FIG. 13, the transmission loss-wavelength waveform substantially matches the target characteristics.
Next, when calculating the total length of the gain equalizer, L = LPG1 + LPG2 = 135.22 mm. Therefore, when the superstructure long-period fiber grating is used, the same characteristics can be obtained with a length less than half.
Furthermore, the conventional gain equalizer requires a plurality of reinforcing members, but in the case of the gain equalizer using the superstructure long-period fiber grating of the present invention, only one reinforcing member is used, which is considerably small. Can be

As described above, in the gain equalizer using the superstructure long-period fiber grating group of the present invention, since the total length of the fiber grating is short and only one reinforcing member is required, the conventional long-period fiber grating and the phase shift length can be reduced. It has been proved that a very small gain equalizer can be provided compared to a gain equalizer using a periodic fiber grating.

Next, an embodiment for controlling the hydrogen loss in the optical fiber to reduce the fluctuation of the center wavelength of the fiber grating will be described.
After the hydrogen treatment that impregnates the optical fiber with hydrogen, first, pre-annealing for removing hydrogen is performed for a certain period. Then, after the grating is formed by irradiating the optical fiber with an ultraviolet laser, annealing for removing hydrogen is performed.

FIG. 6 shows the relationship between pre-annealing time and hydrogen loss when pre-annealing at 80 ° C. by a solid line. The relationship between the pre-annealing time and the fluctuation amount of the center wavelength of the fiber grating is indicated by a broken line. In the graph, the left axis represents hydrogen loss and the unit is dB, and the right axis represents the wavelength shift and the unit is nm. The horizontal axis represents the pre-annealing time, and the unit is time (Hour).

As can be seen from FIG. 6, the hydrogen loss of the optical fiber is suppressed and the fluctuation of the center wavelength of the fiber grating decreases as the pre-annealing time increases.
In particular, pre-annealing is performed so that hydrogen loss at a wavelength near 1244 nm can be controlled. From FIG. 6, the wavelength shift of the fiber grating can be controlled by measuring the hydrogen loss at 1244 nm and determining the pre-annealing conditions so that the hydrogen loss is 0.5 dB / m or less.
Therefore, it can be seen that the wavelength shift of the fiber grating can be controlled by controlling the pre-annealing time so as to obtain a predetermined hydrogen loss.

Next, the following two embodiments will be described with respect to the control method of the fluctuation amount of the center wavelength.

FIG. 7 shows an example in which pre-annealing is performed for 10 hours. In this case, the optical fiber is subjected to hydrogen treatment at a pressure of 15 MPa for one week, and further pre-annealed at 80 ° C. for 10 hours. Next, this optical fiber is irradiated with an ultraviolet laser to form a fiber grating, and then annealing for removing hydrogen and a characteristic stabilization process are performed to form a fiber grating. Further, the irradiation time of the ultraviolet laser is 1 minute.

Here, the characteristic stabilization process is a process shown below.
When no processing is performed on the fiber grating formed by irradiating the ultraviolet laser, the refractive index decreases with time, and deterioration with time occurs in which the center wavelength shifts to the short wavelength side. Therefore, in order to prevent this deterioration with the passage of time, it is effective to perform a process of removing unstable elements in advance by heating the fiber grating portion to a high temperature, which is referred to as a characteristic stabilization process.

The one-dot chain line, the broken line, and the solid line in FIG. 7 indicate waveforms after the ultraviolet laser irradiation, the hydrogen removal annealing, and the characteristic stabilization, respectively. Here, the vertical axis of the graph is transmission (loss), the unit is dB, the horizontal axis is the wavelength, and the unit is nm.

From the comparison of the center wavelengths of the fiber gratings in FIG. 7, the change in the center wavelength after the ultraviolet laser irradiation and after the hydrogen removal annealing is around 30 nm.
Further, in a test conducted by irradiating 10 optical fibers with an ultraviolet laser under the same conditions, the fluctuation amount of the center wavelength after ultraviolet irradiation and after hydrogen removal annealing was 30 nm plus or minus 1.2 nm.

Next, FIG. 8 shows an example in which pre-annealing is performed for 15 hours.
In this case, the optical fiber is subjected to hydrogen treatment at a pressure of 15 MPa for one week, and further pre-annealed at 80 ° C. for 15 hours. Next, this optical fiber is irradiated with an ultraviolet laser to form a fiber grating, and then annealing for removing hydrogen and a characteristic stabilization treatment are performed to form a fiber grating. Here, the irradiation time of ultraviolet rays is 5 minutes.

The one-dot chain line, the broken line, and the solid line in FIG. 8 indicate waveforms after the ultraviolet light irradiation, the hydrogen removal annealing, and the characteristic stabilization, respectively. Here, the vertical and horizontal axes of the graph are the same as those in FIG.

From the comparison of the center wavelengths of the fiber gratings in FIG. 8, the fluctuation amount of the center wavelength after the ultraviolet laser irradiation and after the hydrogen removal annealing is around 5 nm, which is very suppressed.
In a test conducted by irradiating 10 optical fibers with an ultraviolet laser under the same conditions, the fluctuation amount of the center wavelength after ultraviolet irradiation and after hydrogen removal annealing was 5 nm plus or minus 0.2 nm.

It can be seen that the shift of the center wavelength is significantly suppressed by increasing the pre-annealing time as compared with the case of FIG. Accordingly, when an optical fiber in which the increase in hydrogen loss is controlled to 0.15 dB / m is used, wavelength control on the sub-nano order becomes possible.

Next, in order to compare with the method for controlling the pre-annealing time of the present invention, examples in which pre-annealing is not performed and in which hydrogen treatment is not performed are shown.
9 shows a case where an optical fiber is subjected to hydrogen treatment at 15 MPa for one week, pre-annealing is not performed, a fiber grating is formed by irradiation with an ultraviolet laser, and then hydrogen removal annealing and characteristic stabilization treatment are performed. It is. Here, the irradiation time of ultraviolet rays is 30 seconds.

The alternate long and short dash line, broken line, and solid line shown in FIG. Here, the vertical and horizontal axes of the graph are the same as those in FIG.

From the comparison of the center wavelengths of the fiber gratings in FIG. 9, the fluctuation amount of the center wavelength after the ultraviolet irradiation and after the hydrogen removal annealing is a large value of around 90 nm.
In a test conducted by irradiating 10 optical fibers with an ultraviolet laser under the same conditions, the fluctuation amount of the center wavelength after ultraviolet irradiation and after hydrogen removal annealing was 90 nm plus or minus 5 nm.
In the case where this pre-annealing is not performed, no matter what optical fiber is used, it is almost uncontrollable when sub-nano order is required in the wavelength system.

Subsequently, FIG. 10 shows an embodiment in which a fiber grating is formed by using a photosensitive optical fiber and irradiating an ultraviolet laser without performing any hydrogen treatment. Here, the irradiation time of ultraviolet rays is 30 minutes.

The dashed-dotted line, broken line, and solid line in FIG. 10 indicate waveforms after ultraviolet laser irradiation, annealing, and characteristic stabilization, respectively. Here, the vertical and horizontal axes of the graph are the same as those in FIG.

From the waveform of FIG. 10, when the photosensitive fiber is irradiated with ultraviolet rays without hydrogen treatment, the waveform after irradiation is stable. However, the maximum transmission loss is 4 dB. In order to realize this, it is necessary to irradiate ultraviolet rays for 30 minutes, and the productivity is very low.
Furthermore, in this case, sub-nano-order wavelength control is possible, but it is difficult to obtain sufficient transmission loss characteristics.

As described above, when pre-annealing for hydrogen removal as shown in FIGS. 7 and 8 is performed, the pre-annealing as shown in FIG. 9 is not performed, or the hydrogen treatment as shown in FIG. 10 is performed. Compared with the case where it was not performed, it was found that the fluctuation amount of the center wavelength was greatly suppressed, and the ultraviolet irradiation time was shortened, and the effect of the present invention was proved.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various embodiments can be considered.

The figure which shows the structure of a superstructure long period fiber grating. The figure which showed the transmission loss-wavelength waveform of the superstructure long period fiber grating of order N. The figure which showed the transmission loss-wavelength waveform of the superstructure long period fiber grating which made L2 and L1xN constant. The figure which showed the structure of the gain equalizer using a superstructure long period fiber grating. FIG. 5 is a diagram showing a transmission loss-wavelength waveform of a superstructure long-period fiber grating and a gain equalizer having the structure shown in FIG. The figure which shows the relationship between pre-annealing time and hydrogen loss, and pre-annealing time and center wavelength fluctuation | variation. The figure which showed the fluctuation | variation of the center wavelength after ultraviolet laser irradiation and annealing after the pre-annealing time of 10 hours. The figure which showed the fluctuation | variation of the center wavelength after ultraviolet laser irradiation in the case of pre-annealing time 15 hours, and after annealing. The figure which showed the fluctuation | variation of the center wavelength after ultraviolet laser irradiation and the annealing after not performing pre-annealing. The figure which showed the fluctuation | variation of the center wavelength after ultraviolet laser irradiation and annealing after forming a grating without performing hydrogen treatment on a photosensitive fiber. The figure which shows an example of the target transmission loss-wavelength waveform of a gain equalizer. The figure which shows the structure of the gain equalizer using four uniform long period fiber gratings. The figure which showed the transmission loss-wavelength waveform of the long period fiber grating shown in FIG. 12, and a gain equalizer. The figure which shows the structure of the gain equalizer using a uniform long period fiber grating and a phase shift long period fiber grating. The figure which showed the transmission loss-wavelength waveform of the long period fiber grating and gain equalizer which are shown in FIG.

Claims (2)

(1) impregnating the optical fiber with hydrogen by high-pressure hydrogen; (2) performing pre-annealing for a predetermined time during which the concentration of hydrogen contained in the optical fiber decreases to a predetermined concentration; and irradiating the optical fiber with an ultraviolet laser. A step 3 of forming a fiber grating, and a step 4 of performing annealing for removing the hydrogen from the optical fiber ,
Controlling the pre-annealing time so that the fluctuation amount of the center wavelength of the fiber grating after the step 3 and after the step 4 is 10 nm or less,
A method of manufacturing a fiber grating.   2. The method of manufacturing a fiber grating according to claim 1, wherein in the step 1, hydrogen is impregnated into the optical fiber with high-pressure hydrogen of approximately 15 MPa.